Water filtering module with hollow fibers

ABSTRACT

The invention concerns a module for ultrafiltration or microfiltration of water comprising hollow fibers, of the type of filtration from outside inwards of the fibers, the water to be treated being introduced at the top of the module and the treated water being collected at the bottom of the module. The fibers are arranged inside a housing ( 3 ) in multiple U-shaped bundles ( 1 ), the module being vertically arranged in use with the U-shape in the top part of the module. At the bottom of the module, each bundle is arranged in a sheath ( 4 ) and individually potted. The sheaths are then urged to be housed in a distribution plate ( 2 ), and all the sheaths are interconnected by pouring (in reverse vertically position relative to that of the filtering mode) a so-called potting resin ( 5 ).

[0001] The method constituting the subject matter of the presentinvention is from the field of water filters. It relates moreparticularly to the field of ultrafiltration type membrane filters.

[0002] Modules including one or more bundles of hollow fibers stretchedout parallel to each other and alongside each other and potted at boththeir ends are known in the art. With both ends potted and cut, themodules are used in external/internal filtration or vice-versa. Some aremulti-bundle modules, the bundles being assembled with common potting ofall the bundles. When they are used in external/internal filtration, airinjection nozzles are disposed at the bottom of the peripheral bundles.The document EP-0 655 418 discloses an installation of this type.

[0003] Modules including one or more bundles of hollow fibers whose endsare potted at one end and free but closed individually at the other endare also known in the art. With one end potted, the fibers being pluggedindividually at the other end but not potted [sic]. The potted end is atthe top in operation. These modules are used in external/internalfiltration.

[0004] Modules including bundles of hollow fibers with the fibersdisposed in a U-shape and bent at the bottom may also be cited.

[0005] Some modules use multiple bundles arranged in a casing, with amechanical seal provided around the potting around the top of eachbundle (generally by an O-ring). Air can be injected at the bottom ofthe module.

[0006] For all these types of modules, the bundles are either directlypotted in a casing or demountable from the casing, the seal beingprovided by O-rings around the potting.

[0007] Bundles that are not housed in a pressure casing, but in a pool,the permeate being recovered by suction, are also used in the field ofimmersed membrane filters in particular. These modules generally usecompressed air to agitate the bundles, whether this is with a verticalbundle potted at both ends, with air nozzles around the bundle, or witha horizontal bundle potted at both ends, the air being injected byauxiliary means at the bottom of the pool.

[0008] These various filters are complex and costly. They are alsosubject to problems of efficient operation, in particular of correctbubbling.

[0009] An object of the present invention is to provide a simpleultrafiltration or microfiltration module that preferably remedies thesedrawbacks.

[0010] To this end the invention is directed to a module forultrafiltration or microfiltration of water, using hollow fibers, of thetype with filtration from the exterior toward the interior of thefibers, water to be treated being introduced at the top of the moduleand treated water being collected at the bottom of the module,characterized in that the fibers are disposed inside a casing inmultiple bundles in which the top portion of each fiber is free, thecasing envelops the bundles to hold them in position, and, at the bottomof the module, each bundle is disposed in a sheath and pottedindividually, with the bundles then accommodated in a distributionplate.

[0011] The distribution plate can advantageously also be used to injectair into the module.

[0012] In a preferred embodiment of the invention the fibers aredisposed inside a casing in multiple U-shaped bundles, with the branchesof the U-shape disposed vertically in use with the base of the U-shapeat the top of the module. Each bundle, and thus also each fiber, istherefore of inverted U-shape in use.

[0013] Clearly this enables a multi-bundle U-shape arrangement, with thebase of the U-shape of the bundles at the top. It also providesefficient bubbling.

[0014] Furthermore, this arrangement authorizes use of the module forimmersed gravity filtration, in particular with minimal chemicalcleaning volumes and above all the facility, in an immersed membranebioreactor, to return the chemical cleaning residues to the pool andthus dilute it and treat it in the pool itself.

[0015] It is also clear that this U-shaped arrangement with the bend atthe top of the module means that a defective bundle can be taken out ofservice.

[0016] This arrangement also greatly facilitates the fabrication of alarge module.

[0017] The sheaths are preferably all connected together by pouring atwo-component potting resin (in a vertical position which is the reverseof that used in the filtration mode).

[0018] For example, the distribution plate is provided with air passagesdischarging axially between the sheaths. These air passages can be fedradially from the periphery of the distribution plate.

[0019] In a preferred embodiment, the casing is closed at the top andsealed by a connection plate having a bore, for example a threaded bore,for connecting a supply of water to be filtered.

[0020] The upper part of the casing is advantageously also provided withlifting holes.

[0021] The following description, and the accompanying drawing, explainthe objects and advantages of the invention more clearly. It is clearthat the description is given by way of example only and has no limitingcharacter. In the drawing:

[0022]FIG. 1 shows diagrammatically a water filter in accordance withthe invention, in longitudinal section taken along the section line I-Iin FIG. 2, and

[0023]FIG. 2 shows the same installation in cross section taken alongthe section line II-II in FIG. 1.

[0024] As shown in FIG. 1, the filter according to the invention is anultrafiltration or microfiltration module with hollow fibers, of thetype with filtration from the exterior toward the interior of thefibers, with or without backwashing. It is intended to be used, forexample, in a water purification installation using a gravity differenceas a source of pressure for passing water through the wall of themembranes.

[0025] The water to be treated is introduced via the top of the moduleand the treated water is collected at the bottom of the module.

[0026] The fibers are disposed inside a casing 3 in multiple U-shapedbundles 1, the module being disposed vertically in use, with the base ofthe U-shape at the top of the module. The fibers and bundles thereforeform inverted U-shapes.

[0027] The casing 3 envelops the hollow fibers disposed in bundles 1 tohold them in the position described. Little space is left, on the onehand, between the bundles, or the branches thereof and, on the otherhand, between the bundles and the casing. The fibers are thereforelightly pressed together to retain them and the casing 3 retains thefibers and bundles at the periphery.

[0028] The casing is made from a circular cylindrical polyvinyl chloride(PVC) tube. It contains, for example, nineteen bundles 1 of fibers inthe embodiment shown in the drawing. Its diameter is then approximately300 mm for a length of approximately 1 000 mm. These dimensions aregiven by way of example only.

[0029] At the bottom of the module, each bundle 1 is disposed in asheath 4 and individually potted. The sheaths are then accommodated in adistribution plate 2.

[0030] Each sheath 4 takes the form of a circular cylindrical sleeve,for example. The two free ends of the same fiber bent into an invertedU-shape are always in the same sheath. The distribution plate 2 hasbores through it whose inside diameter corresponds to the outsidediameter of the sheaths 4. A flange is provided at one end of eachsheath, on the outside, to limit the sliding of the sheath 4 in thecorresponding bore and to enable correct positioning of the sheath 4relative to the distribution plate 2.

[0031] Each sheath is made of polyvinyl chloride (PVC), for example. Inthe preceding numerical example, the sheaths can have an inside diameterof 52 mm and a height of approximately 100 mm.

[0032] Finally, all the sheaths are joined together by pouring atwo-component potting resin 5 (in the vertical position that is thereverse of that used in the filtration mode). The resin provides theseal between the high-pressure portion and the low-pressure portion ofthe filter.

[0033] An identical potting resin is used to provide the seal betweenthe fibers of the same bundle 1 in the sheaths 4.

[0034] Moreover, the distribution plate 2 is provided with passages 8for air introduced via a lateral orifice 9 at the bottom of the module.The passages 8 are oriented axially and radial passages 10 connected toa peripheral passage 11 supply them with air from the lateral orifice 9.The air is evacuated in the form of ascending bubbles that agitate thebundles to improve the elimination of filter cake formed on the fibers.

[0035] The casing 3 is closed at the top by a connection plate 6. Thisis mounted on and sealed to the opposite end of the distribution plate2. A threaded bore 12 at the center of the connection plate 6 is used toconnect a pipe (not shown) for supplying water to be treated.

[0036] The resulting assembly is a filtration module in which water tobe treated is introduced at the top and filtered water is recovered atthe bottom. The sealed module forms a filter unit. In addition to manyother functions, the casing 3 guides the water to be treated. Bydelimiting a confined space around the fibers, the casing 3 contributesto the many advantages of the filter described above.

[0037] The advantages of this design in use are the multi-bundledisposition that minimizes the problems of poor access to the filtrationsurface and the difficulty of cleaning the fibers.

[0038] Thanks to the U-shaped configuration, there are spaces betweenthe bundles, on the one hand, and in the middle of each bundle, on theother hand.

[0039] Moreover, air can be injected between the bundles, the airbubbles flowing mainly tangentially to the bundles.

[0040] The configuration of this module:

[0041] a) does not deflect the path of the air bubbles which agitate thebundles,

[0042] b) purges air efficiently from the module, especially on firststarting operation, but also when bubbling is effected duringfiltration,

[0043] c) does not divert the flow of the filter cake debris evacuatedby the bubbles and/or by the backwashing water,

[0044] d) naturally allows the bundle to form a belly, at around themiddle height, which also improves the flow from the exterior to theinterior of the bundle (filtration direction) or vice-versa (backwashingdirection). In association with the air, this therefore increasesturbulence near the bundles, which is favorable from the point of viewof limiting clogging,

[0045] e) avoids (costly) potting at one end, and

[0046] f) means that, if a fiber breaks, after the defective bundle isidentified, it can either be repaired (as is the usual practice), or theincriminated bundle can be taken out of service by fitting a cap gluedto the end of the sheath of the bundle, for example.

[0047] It is also possible to work with gravity filtration by connectingthe connection plate 6 to the water to be treated under pressure.

[0048] It is also possible to operate in an “immersed membrane” mode,with the plate 6 not connected. In this case, chemical cleaning can beeffected and is limited to filling the module with cleaning solution viathe connection plate up to the top. This limits the volume of cleaningsolution to the strict minimum, i.e. the volume of the module.

[0049] Handling is facilitated by the presence of lifting holes 7 at thetop of the module.

[0050] Manipulation during fabrication is easy. The individual bundlesare sheathed with a flexible elastic film sheath which is used duringindividual potting of the bundles and removed when the bundle and itssheath are fitted to the distribution plate.

[0051] The bundles (in fact their sheaths) are fitted to thedistribution plate in a vertical position, with the base of the U-shapeat the bottom, after which the combination of the bundles and thedistribution plate is introduced into the casing. The whole is thenpotted.

[0052] Potting is simplified because even for large modules (100 m²filter area and above), there is no utility in carrying out theinevitably complex simultaneous potting of several tens of thousands offibers. Potting is effected on small individual bundles. Testing eachbundle beforehand eliminates the risk of having to scrap a casing andits peripheral components because of a few damaged fibers.

[0053] The connection plate 6 is then glued (or welded) into the casing3.

[0054] The air supply system is simple, with no nozzles, which could inany event damage the bundles.

[0055] Note that an important advantage of the filter according to theinvention is the possibility of injecting air by means of thedistribution plate 2, which therefore has several roles.

[0056] Moreover, backwashing (by circulating water through the membranesin the reverse direction to clean them) can be effected with water butalso with air if the diameter of the pores is sufficient, for example inthe case of microfiltration.

[0057] Clearly the geometry chosen for the filter according to theinvention enables a defective bundle to be identified easily: forexample, by injecting air from the untreated water side, with the modulein an inverted vertical position and with water on the distributionplate 2, so that bubbles can be seen escaping from the defective bundle.

[0058] Consideration can then be given either to plugging the defectivefiber or fibers, using conventional means known to the person skilled inthe art, or to isolating the entire bundle permanently, for example bygluing on a plug, or reversibly, by fitting a removable plug, pendingthe simultaneous execution of several repairs.

[0059] Plugging one or more bundles of fibers does not interfere in anyway with the operation of the module as a whole.

[0060] The scope of the present invention is not limited to the detailsof the embodiments described above by way of example, but to thecontrary extends to modifications that will be evident to the personskilled in the art.

[0061] For example, instead of U-shaped bundles of fibers, fibers can beused whose upper portion is plugged but free.

1. A module for ultrafiltration or microfiltration of water, usinghollow fibers, of the type with filtration from the exterior toward theinterior of the fibers, water to be treated being introduced at the topof the module and treated water being collected at the bottom of themodule, characterized in that the fibers are disposed inside a casing(3) in multiple bundles (1) in which the top portion of each fiber isfree, the casing (3) envelops the bundles to hold them in position, and,at the bottom of the module, each bundle is disposed in a sheath (4) andpotted individually, with the bundles then accommodated in adistribution plate (2).
 2. A module according to claim 1, characterizedin that the distribution plate (2) is used to inject air into the module(1).
 3. A module according to either claim 1 or claim 2, characterizedin that the fibers are disposed inside a casing (3) in multiple U-shapedbundles (1), with the branches of the U-shape disposed vertically in usewith the base of the U-shape at the top of the module.
 4. A moduleaccording to any of claims 1 to 3, characterized in that all the sheathsare interconnected by a two-component potting resin (5).
 5. A moduleaccording to any of claims 1 to 4, characterized in that thedistribution plate includes air supply passages discharging axiallybetween the sheaths.
 6. A module according to claim 5, characterized inthat the air passages are fed radially from the periphery of thedistribution plate.
 7. A module according to any of claims 1 to 6,characterized in that the casing (3) is closed at the top and sealed bya connection plate (6) having a bore (12) for connecting a supply ofwater to be filtered.
 8. A module according to claim 7, characterized inthat the bore (12) for connecting a supply of water to be filtered isthreaded.
 9. A module according to any of claims 1 to 8, characterizedin that the casing (3) has lifting holes (7) at the top.